Life at the edge of dryness

Imagine a desert that is not hot. In the Atacama, along the coast of northern Chile, average summer temperatures in a town like Iquique are only about 19 °C, according to Encyclopaedia Britannica. Fog often hangs along the coast. And yet this is one of the driest places on Earth. NASA notes that some parts of the desert have not seen rain for centuries.

A long, narrow desert

Britannica describes the Atacama as a cool, arid region in northern Chile, about 1,000 to 1,100 kilometres long from north to south. It lies between the Pacific Ocean and the Andes, with a coastal mountain chain that mostly reaches around 1,500 metres.

It is also old. NASA’s astrobiology programme notes that the desert is roughly 10 to 15 million years old.

Why it hardly ever rains

Several forces work together to keep the Atacama dry.

The first is the ocean. Along the coast, the Peru Current — also called the Humboldt Current — brings cold water up from the deep. Cold water cools the air above it, and cool air near the surface does not rise easily to form rain clouds. Britannica notes that this produces fog and low stratus clouds, but no rain.

The second is the atmosphere. Britannica points to dry, sinking air created by the South Pacific high-pressure system, which suppresses the rising air that rain needs.

Rain does sometimes reach coastal towns such as Iquique and Antofagasta, Britannica explains, but only occasionally, when storm systems move in from the south.

Can anything live here?

In the driest parts of the Atacama, life is very hard to find. When NASA-funded researchers sampled the soil, they found only small numbers of bacteria in some places, and none of the cyanobacteria that are common in other deserts. As NASA put it, water is so scarce in the Atacama that it is a wonder anything can live there at all. The scientists did not even know what the bacteria they found were eating, or where they got their water.

That is exactly what makes the place interesting.

A rehearsal for Mars

Scientists use the Atacama to study how dryness limits life. NASA describes the desert as a place that can help answer an important question about Mars: how does extreme dryness affect life?

The comparison has limits. Mars is far colder — NASA gives its average temperature as about −69 °C, while the Atacama ranges from about 0 to 23 °C. But on Earth, few places come closer to Martian dryness. Instruments and methods designed to search for life on other planets are tested here first. If a technique cannot find life in the Atacama, where we know some exists, it is unlikely to succeed on Mars.

People in the desert

The Atacama is not empty of people. Britannica notes that the region’s original inhabitants were the Atacameños. Later the desert became a source of mineral wealth: before the First World War, Chile held a near-monopoly on natural nitrate, and in some years three million tons were extracted. Today the region’s chief source of income is copper mining, especially at Chuquicamata.

Why it matters

The Atacama shows how far the limits of life can be pushed — and where they finally are. It is a natural laboratory for questions about our own planet’s past and about life elsewhere. A place where it almost never rains turns out to be full of answers.